Some examples of small telephone systems have been generally referred to as key telephone systems. Traditionally a key telephone system is provided by extensive telephone line and control lead wiring between key telephone sets. Each key telephone line extends to a telephone exchange. Each of the telephone sets includes a plurality of push button switches or keys, each for connecting the telephone set to a particular telephone line among a plurality of telephone lines routed to the key telephone set. The switching function of line selection is mechanically provided and distributed among the key telephone sets. Any features in addition to plain ordinary telephone service (POTS) must be added on a per line basis. The primary advantage of these systems is economy with small size. However, if such a system is required to expand along with the organization it serves, over a time it eventually becomes more expensive on a per line and feature basis than a private branch exchange would be. Key telephone systems are also characteristically of the analog signal type, and therefore are impractical to interface with an ISDN as will likely be desired by business customers in the near future.
So far as those aspects of the invention concerned with replacement and/or relocation in telecommunications systems generally are concerned, most telephone sets or other terminal apparatus nowadays are connected into the system by jacks, so it is a simple matter for the user to unplug a terminal apparatus and reconnect it at a different port. Of course, if those attributes of the terminal apparatus not resident in the terminal apparatus itself are to be retained, corresponding administrative changes must be made at the switch or, in the case of a key telephone system, at the key switch unit. Existing systems require the intervention of a skilled craftsperson to effect such changes, typically by locating the feature set of the terminal apparatus at the vacated port and assigning it to the new port. This involves high costs and may incur delays. A similar situation arises if the user replaces the terminal apparatus with a new set i.e. new to the system rather than being relocated from another port. Usually this would be done to replace a defective set. Providing that they are of the same type, the new set will need to inherit the old set's administration data and, where applicable, intercom number.